The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Motor vehicle automatic transmissions must and do provide both reliable torque multiplication and torque and speed matching over a wide range of both ambient and operating temperatures. The operating temperature of an automatic transmission may be considered to range from cold, i.e., a winter morning start, through warm, i.e., normal operation, to hot, i.e., maximum operating temperature. The fluid within a transmission, commonly referred to as “automatic transmission fluid” or ATF, contracts when it is cold and expands when it is hot. Thus, the noted temperature limits correspond to the minimum and maximum volumes of transmission fluid for a given mass of transmission fluid.
The minimum design or start up temperature dictates the minimum mass of transmission fluid required in the transmission. Under this operating condition, the transmission fluid is most dense which reduces the volume of transmission fluid within the transmission sump and transmission and the viscosity of the fluid is at a maximum thereby further reducing sump and transmission fluid volume due to fluid coating or adhering to transmission components and surfaces.
The maximum design or operating temperature dictates the maximum transmission sump fluid volume which maintains a fluid level below the rotating components of the transmission. If the transmission fluid contacts the rotating components, the fluid will become foamy with entrained air which increases frictional drag and adds heat to the transmission fluid. Eventually, the entrained air will interfere with the action of the transmission pump, transmission fluid pressure will drop, forcing a transmission shutdown and possibly causing damage to the transmission.
It is therefore apparent that the automatic transmission and transmission fluid cooling system must accommodate the cold and, more significantly, the hot volume of transmission fluid, while maintaining intended and desired vehicle performance. This requirement, in addition to the requirements of various vehicle ride heights, suspension components and various engine configurations have proliferated the number of transmission oil (ATF) pans and filter/pump pickups for the same model of automatic transmission.
The present invention is directed to an apparatus for accommodating the volume change of transmission fluid from cold to hot while maintaining proper transmission sump and operating levels.